FIG. 1 illustrates two components contained within a gas turbine engine (not shown), namely, a first, cylindrical, component 3 and a second component 6 separated by a gap 9 from the first component 3. The second component 6 bears hole 12 having a counterbored recess 15. A mast 18 extends through the hole 12 and contains a shoulder 21 which fits into the counterbored recess 15. The mast 18 supports a probe 24 which produces a signal which must be transmitted across the gap 9.
The signal transmission is commonly accomplished through a tube 27, which extends through the mast 18 and reaches the gap 9. If the signal is a pressure signal, the transmission takes the form of a change in pressure in the tube 27 which is read by sensing equipment (not shown). If the signal is electrical, as from a temperature sensor, the transmission is carried along wires contained within the tube 27. Sensing equipment (again, not shown) reads the electrical signal.
A problem in aligning the cylinder 3 with the hole 12 arises from two causes. One, manufacturing inaccuracies and stack-up tolerances almost inevitably cause the cylinder 3 and the hole 12 to become noncoaxial with respect to axis 11. Two, even if the cylinder 3 and the hole 12 are successfully manufactured to be coaxial, differential thermal expansion during engine operation causes the hole 12 and the cylinder 3 to become misaligned.
The misalignment is accommodated by the addition of a helical coil 30 in the tube. The helical coil accommodates dimensional changes occurring between the cylinder 3 and the second component 6 through bending. One end 33 of the helical coil 30 is affixed to a bushing 36 which is brazed into the cylinder 3 at points 39. The other end 42 of the helical coil 30 is affixed to the inside of the shoulder 21.
During manufacture, the helical coil 30 is compressed slightly during installation into the position shown in FIG. 1. Thus, the helical coil 30 acts as a spring to urge the shoulder 21 into contact with the bottom 45 of the recess 15. (The shoulder 21 functions to prevent the mast 18 from falling out of the hole 12 as shown by phantom mast 48 in the event that the tube 27 should break at point 51.)
However, the use of the helical coil 30 has raised a problem. Applicant has found that the helical coil 30 sometimes cracks at elbows 53. These elbows 53 have sharp curvature (approximately 90.degree.) and are termed inflection points at which the tube 27 changes direction from traveling along a helix to traveling along the axis 11.